1. Field of the Invention
The present invention relates to a binocular, and more particularly, to a binocular where pupil distance adjustment and dioptric power adjustment can be automatically set for a specific user.
2. Description of the Prior Art
In a binocular, it is desirable that a pupil distance adjustment and a dioptric power adjustment based on a difference in dioptric power among users are possible, since a pupil distance and a dioptric power differ from user to user.
Japanese laid-open Patent Application S50-153952 discloses a technology to manually adjust a pupil distance and a dioptric power. Japanese laid-open Patent Application S63-161424 discloses a pupil distance adjusting apparatus where the distance between objective lenses are fixed and the distance between eyepieces are manually changed.
In a binocular, generally, pupil distance adjustment is made only by hand. Concerning dioptric power adjustment, however, Japanese laid-open Patent Application S63-206731 discloses a method of automatically making it.
A binocular is frequently used by a plurality of persons (for example, by family member such as father, children, etc.). In view of such a situation, a binocular has been proposed where each user remembers a value or a position of a graduation corresponding to his or her pupil distance, and in using the binocular, the user turns a dial to the value or the position of the graduation, and then, the movement of a lens barrel stops and the pupil distance is set. Moreover, Japanese laid-open Patent Application S50-99750 discloses a binocular where the dioptric power positions of a plurality of users are mechanically stored.
However, since the pupil distance is manually adjusted and the dioptric power is mechanically stored according to these methods, respectively, the adjustments cannot easily and quickly be made. Further, the remembered value or position of a pupil distance and the stored dioptric power positions cannot be utilized for another binocular.
Since the dioptric power adjustment is difficult, it is desirable that it be automatically made. Moreover, concerning the pupil distance adjustment, it is convenient if the pupil distance is automatically adjusted to the pupil distance of a user.
However, if pupil distance adjustment and dioptric power adjustment can be made at random without an order of the adjustments, the adjustments are not quickly made and the eyes are burdened.
In pupil distance adjustment, the left and right optical systems move in directions opposite to each other (that is, to the left and right) in order to increase and decrease the pupil distance. If a TTL (through the lens) method is used where light having passed through the objective lens is used for focus detection for causing a dioptric power so that an in-focus image is viewed by a user (this operation will hereinafter be referred to as AF [automatic focusing] to distinguish it from the above-mentioned dioptric power adjustment based on a user's dioptric power), the length of an optical path to a focus detecting sensor varies when the optical systems move to the left and right. As a result, detection accuracy varies.